C. Xhoffer

Microanalysis of individual environmental particles. Plenary lecture

Applications of instrumental microanalysis techniques for the characterization of individual particles in environmental samples are reviewed. The principles of electron microprobe analysis and related techniques, the micro-version of proton-induced X-ray emission, laser microprobe mass spectrometry, secondary ion mass spectrometry and Raman microprobe analysis, are briefly reviewed and their published applications to aerosols and to aqueous suspensions are described.

Sources and composition of aerosol from Khartoum, Sudan

Abstract Aerosol sampling was carried out during December 1989 in Khartoum, Sudan, using Nuclepore membrane filters. Twenty-four aerosol samples were collected and analysed by X-ray fluorescence (XRF) spectrometry and particle-induced X-ray emission (PIXE). In addition, individual particle analysis was also performed on 19 samples using electron probe X-ray microanalysis (EPXMA). Good agreement between XRF and PIXE results was obtained for most of the elements. Enrichment factor calculations indicated that soil dispersion is the dominant source for most elements in the aerosol. However, certain elements showed high enrichment factors indicating the presence of anthropogenic sources. From a comparison with available literature data it appeared that the enrichment factors for the enriched elements in the Khartoum aerosol are among the lowest recorded values for urban aerosol. Absolute principal components analysis (APCA) was performed on the data and confirmed the findings from the enrichment factor calculations, i.e. a dominant soil dispersion source and an anthropogenic source for some of the elements. Because of the very limited number of impotant aerosol sources, the data set was reporduced by the APCA model with a reasonable degree of success. Single particle analysis also showed that most of the particles were soil dust. These particles could further be differentiated into alumino-silicates, quartz and CaCO 3 particles. Some of the particles were found to originate from combustion sources. EPXMA gave clues to the process of formation for some of the particles from combustion sources.

Electron energy-loss spectroscopy and electron probe X-ray microanalysis of exhaust aerosols in slurry nebulization inductively coupled plasma atomic spectrometry for ceramic powders

Abstract Exhaust aerosols in inductively coupled plasma (ICP) atomic spectrometry generated from different ceramic powder suspensions (Al 2 O 3 , ZrO 2 and SiC) were investigated by electron energy loss spectroscopy (EELS) and electron probe X-ray micro analysis (EPXMA). Differences in morphology, size and elemental composition of sub-micrometer residues of these refractory powders, collected above ICPs operated with different gasses, were found to depend on the outer gas (N 2 O 2 and Ar), the distance between the impacting stage and the plasma, and on the ceramic powder introduced as a slurry into a suitable nebulizer. Identical exhaust types of particles were observed in the case of Al 2 O 2 and ZrO 2 slurries, also when different outer gases and different operation conditions were used. For SiC, much depends on the outer gas used, as shown by morphological and chemical composition studies. Electron energy loss spectroscopy and element spectroscopic imaging (ESI) were used for the elemental analysis and the localization of the detected elements (Al, Zr, Si, C, O and N) in the individual exhaust particles.

A method for the characterization of surface-modified asbestos fibres by electron energy-loss spectroscopy and electron spectroscopic imaging

A method for the characterization of surface‐treated asbestos fibres with electron microscopy is presented. Electron spectroscopic imaging (ESI) of organosilane‐treated chrysotile asbestos fibres has been carried out. Initially, the region below the carbon edge was inspected in ESI mode for its effectiveness as a background correction. Elemental mapping was performed on standard untreated fibres to take into account non‐characteristic signals from extrapolation errors and camera artefacts. The highest resulting pixel value that results from non‐characteristic signals was used as a threshold for further background correction in the net images. Samples for electron energy‐loss spectroscopy were prepared in two different ways, either by gluing on grids, or by using perforated carbon foils. The results show that the use of a conducting carbon film is necessary for the analysis of such electrically insulating asbestos fibres. Focusing of the electron beam on the individual fibres results in a thermal effect promoting the evaporation of the organosilane reaction products.

Problems in quantitatively analyzing individual salt aerosol particles using electron energy loss spectroscopy

Polydisperse standard aerosols of NaCl, (NH4)2SO4 and KNO3 have been generated from their solutions by pneumatic nebulization. These aerosol particles are electron beam sensitive and therefore special precautions are necessary. A methodology is proposed for serially recording electron energy loss spectra (EELS) from sub-micrometer salt particles. The results of quantification are compared with those obtained by parallel electron energy loss spectroscopy (PEELS). Experimental conditions such as the intensity of the primary beam, time of radiation and temperature are responsible for large deviations from the theoretical values. These deviations arise because heavy mass losses occur, especially during the serial spectrum acquisition. The more time consuming serial EELS is therefore at a disadvantage relative to the parallel method. The best results are obtained for NaCl because the halogen loss can be reduced more efficiently than nitrogen and oxygen losses. The results show that nitrogen loss occurs within the first few seconds of the experiment at normal radiation doses. Even at cryogenic temperatures, losses of volatile elements cannot be avoided.